The present invention relates generally to material handling systems and, more particularly, to controlling a vacuum generator for suction cups of material handling systems that are engaged with the objects and substantially sealed thereto via operation of the vacuum system comprising the vacuum generator and the suction cups. It is known to provide a material handling system that includes suction cups or the like that are adapted to be moved into engagement with an object, such as a substantially flat object or panel or the like, and to lift and move the object to a desired location. The suction cups may be moved into engagement with the object, and the vacuum generator may be actuated to create a vacuum between the object and a suction cup such that the object is retained to the suction cup as it is transported to the desired location.
The vacuum generated at the suction cup(s) is provided by the vacuum generator in the vacuum system, whereby pressurized air is supplied or provided to the vacuum generator.
When the air supply to the vacuum generator is deactivated, such that no vacuum is generated, the vacuum in the vacuum system may dissipate through a vent that connects the vacuum system to an atmosphere outside of the system, and when the vacuum has dissipated in the system and in the cup, to a sufficient amount, the suction cup may be released from the object.
Prior art devices are known from e.g. EP-1064464 where it is disclosed a vacuum ejector pump for generating a negative pressure used for transportation or lifting purposes. And in, U.S. Pat. No. 7,950,422 where it is disclosed an auto-release vacuum device for a material handling system.
It is known, in order to reduce cycle times in industrial production lines, to provide vacuum generators having arrangements for the active release of objects from the suction cup(s).
Prior art devices are known from e.g. EP-B1-2263011 where it is disclosed a vacuum generator, driven by high-pressure air, and having means arranged for active release of an object that is gripped by means of a suction cup.
Active release can for instance be provided by means of activating so-called “blow off”. Blow-off means actively supplying compressed air into the vacuum system to release an object that is gripped by means of a suction cup.
Blow-off using compressed air is expensive in terms of energy-use due to the fact that there is a consumption of compressed air and also in terms of increased cycle time due to the fact that blow-off takes time. Nevertheless, blow-off has to be activated a period of time long enough for the object to be released, but preferably as short as possible to save energy and reduce cycle-time.
Therefore, normally blow-off is set a fixed time in the vacuum system, but to ensure that the period of time blow-off is activated is still long enough for the object to be released, blow-off is normally activated longer than necessary to ensure that the object is released consistently for each cycle.
Also other factors of the vacuum system influence blow-off activation duration. For instance gripper designs vary a lot which influences the blow-off efficiency as well as blow-off activation duration. Other factors that influence are for instance: dimensions of vacuum channels, volume of channels and other parts of the vacuum system.
Also the number of suction points influence, as well as compressed air injection point for blow-off.
A problem is that sensing vacuum pressure in each suction point requires multiple vacuum sensors and typically complex data management.
An object of the present invention is to provide a method, control unit and vacuum system for controlling a vacuum ejector device that eliminates, or at least mitigates, the above stated drawbacks.